Evaporative Emission System Vent Valve Control Circuit High
The P0499 code means the vehicle's onboard diagnostic system has detected: Evaporative Emission System Vent Valve Control Circuit High. This is a low severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- moderate
- Estimated cost
- $50 - $250 (parts and labor)
A cracked or loose gas cap causes 60%+ of EVAP codes. This $8 replacement clears P0442, P0455, and P0457 more often than any other repair.
If a new gas cap does not clear it, the leak is somewhere in the EVAP plumbing. A smoke machine finds the exact leak -- a cracked hose, bad seal, or stuck vent valve -- in minutes instead of guessing at parts.
Clear the code after the repair. If the light stays off after 50 miles, you just saved $200+ in shop fees.
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Common Symptoms
- Check Engine Light on
- EVAP system unable to seal for leak test
- Fuel vapor odor
- Failed emissions test
Probable Causes (Ranked by Likelihood)
- Short to power in vent valve control wiring Very High
- Vent valve solenoid stuck energized (closed) High
- Wiring harness damage near charcoal canister area Moderate
- ECM vent valve control driver stuck high Low
Common Fixes by Vehicle
What techs usually find when diagnosing P0499 on specific vehicles — tap your vehicle for the fix and the exact part:
2008-2016 Nissan Altima/Maxima 2.5L/3.5L moderate DIY
P0499 on Nissan = EVAP vent control circuit high voltage. The vent valve is at the rear of the vehicle on the EVAP canister. The valve solenoid opens internally causing a high-side circuit fault. Replace the vent valve with Nissan or equivalent. Inspect the vapor lines for damage from debris -- these run along the frame rail. Confirm the exact part for your year and engine with a retailer's fitment lookup or your VIN before ordering - these applications split by engine and build date.
Labor: 1 hour2005-2014 Toyota Tacoma/4Runner 4.0L moderate DIY
P0499 on Toyota trucks is the EVAP canister vent valve assembly (Toyota calls it the 'CCV'). Spider webs, mud, and road debris block the air filter on top of the valve, causing a pressure/circuit fault. Clean or replace the valve and its filter. Also verify the fuel tank pressure sensor reads 0 inHg at rest.
Labor: 1 hour2011-2018 Ford F-150 3.5L EcoBoost/5.0L moderate DIY
F-150 P0499 points to the EVAP vent solenoid (Ford calls it the Canister Vent Solenoid, CVS) on the canister behind the rear wheel. Motorcraft is the correct replacement. A failed CVS will also trigger a gas-cap-like no-start EVAP warning on the cluster. Reset adaptive values after replacement with FORScan. Confirm the exact part for your year and engine with a retailer's fitment lookup or your VIN before ordering - these applications split by engine and build date.
Labor: 45 minFrequently Asked Questions
What does circuit high mean for P0499?
Circuit high means the ECM detects higher-than-expected voltage on the vent valve control circuit. This typically means the solenoid is receiving constant power, keeping it energized (closed) when it should be open.
Can a stuck vent valve cause fuel tank pressure issues?
Yes. If the vent valve is stuck closed, air cannot enter the charcoal canister. This can create a vacuum in the fuel tank during fuel consumption, potentially causing fuel pump strain and difficulty refueling.
Can I hear the vent valve operating?
Yes. When commanded by the ECM, you can usually hear a quiet click from the vent valve solenoid. If you command it with a scan tool and hear no click, the solenoid is likely stuck or the circuit is not reaching the valve.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
-
Disconnect the vent valve connector and check for voltage on the control wire with key off; voltage present indicates a short to power
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Test the vent valve solenoid for proper resistance and mechanical operation
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Inspect wiring from ECM to vent valve for chafing or damage from road debris
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Command the vent valve open and closed using a scan tool to verify ECM can control it
Sources 2
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
- Cross-checked against the SAE J2012:2002 DTC table (2026-08-27)archived scan of the SAE standard — readable copy, not SAE’s current edition
Commonly Affected Vehicles
- 2010-2020 Nissan Sentra
- 2012-2019 Kia Optima
- 2008-2018 Chevrolet Cruze
- 2011-2020 Mazda3
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